Influence of processing aids on the thermal and photostabilisation of HDPEwith antioxidant blends

The thermal and photostabilising performances of two commercial phenol/phos phite (Anox-Great Lakes) and three commercial phenol/phosphite/lactone (Cib a Specialty Chemicals) packages have been determined in HDPE in the absence and presence of two processing aids, calcium stearate and oleamide. Stabil ities were assessed using FTIR, thermal analysis and mechanical property ch anges (tensile, elongation and impact). In terms of thermal stabilisation t he phenol/phosphite blends are found to be superior to the Trisphenol/phosp hite/lactone blends. Solid-state (oven ageing) and melt (OIT) stabilities w ere found to follow a similar trend as does the yellowness index. The Anox blends were found to offer superior stability in terms of oxidative and mec hanical performance. Colour inhibition was strong except in the case of cal cium stearate. However, in the presence of calcium stearate strong synergis m was observed with the Irganox blends and this may be associated with an e xchange interaction/complexation between the calcium and the lactone/phosph ite derivatives. These complexes appear to have high performance in thermal stabilization possibly through hydroperoxide decomposition and inhibition of carbonyl formation. In contrast, the effects of photostabilisation were significantly different with strong antagonistic effects in the presence of the calcium stearate due to the instabilities of any calcium complexes. Ov erall, the chemical and mechanical property changes followed a similar patt ern. (C) 2001 Elsevier Science Ltd. All rights reserved.